This invention relates to a needle selecting device in a circular knitting machine. More particularly, the invention relates to those machines which are equipped with oscillating needle pusher jacks, wherein the selection is effected through the engagement of a tooth of a toothed selection disk with a pattern butt of a needle pusher jack, thus causing the jack to move into an inoperative position wherein it is not raised and does not lift the overlying needle into its thread pick up position at a given feed, the toothed disk being rotated by a coaxial entraining disk at a rotational speed such as to produce a substantially rolling action between the needle cylinder and toothed disk, and being angularly displaceable with respect to the entraining disk between an angular position corresponding to said engagement and an angular position of no engagement, a lever being provided for the angular displacement action having a hooked end which can be controllably inserted between the teeth of the toothed disk to temporarily stop the toothed disk rotational movement with respect to the entraining disk against the bias of a resilient means placed between the toothed disk and entraining disk.
A device of this type is disclosed in Italian Patent No. 811,297. Two embodiments are described in that patent, being applied to a hose knitting machine with rotating needle cylinder. In a first embodiment, the arrangement is such that during the normal rotation of the two disks, without the hooked lever coming into operation, each tooth of the toothed disk is pressing against a corresponding butt, of a jack, thereby the jack is commonly shifted to an inoperative position, while the braking action of the hooked lever leads each time to a temporary phase displacement with respect to the position of normal rotation for a time length as required to prevent an interaction between one tooth of the toothed disk and the butt of the corresponding jack from occurring, thus holding the jack in an operative position, wherefrom it is then lifted to cause the overlying needle to pick up the thread of the successive feed. The contrary happens instead in the second of such embodiments, i.e. in the normal entrainment condition there exists a phase displacement of the tooth and corresponding jack butt, which prevents their mutual engagement, thereby the jacks are commonly held in an operative position, while the temporary braking action of the hooked lever each time brings about an angular displacement such as to cause one tooth to interact with a butt for a sufficient time to effect the displacement to an inoperative position of the corresponding jack during the rotation of the entraining disk.
Thus, the programmed control of the hooked lever, bringing about an angular phase displacement of the toothed disk with respect to the rotatable entraining disk, permits in both embodiments alternation of the conditions of interaction between teeth and butts, thereby obtaining a determined selection.
The entrainment of the toothed disk is effected by means of a pin, rigid with the entraining disk and inserted through a circular opening in the toothed disk having a diameter appreciably larger than the pin diameter, thereby the two angular positions described above are defined by the pin engaging with a point on the circumference of the opening which is advanced or leading, and respectively retarded or following, relative to the pin direction of motion.
According to a particular feature, the hooked lever is subjected to the action of a spring, which tends to hold the lever with its hook in contact with the toothed disk, and is controlled by a solenoid which, when activated, pulls the lever against the spring bias to a position such as to hold the hook disengaged from the teeth of the toothed disk, thus maintaining the normal conditions of rotation of the two disks, and when de-activated releases the lever under the spring bias to the position of engagement with the toothed disk to create the stop condition of that disk. The activation and de-activation of the solenoid may be suitably controlled through a punched card system, implemented in conformity with the selection to be carried out, i.e. the pattern that is desired in the resulting knitwork.
The basic advantage of this device is that it allows the selection to be varied at will, since the selection is effected electrically and accordingly easily adjusted as desired, for instance by simply replacing the punched cards of the selection program. To this effect, the selection system is, at least in theory, far more advantageous than the systems providing pattern disks or drums having teeth arranged to suit the selection program, and wherein it is necessary to replace physically a whole set of disks or the entire drums each time the knitwork pattern is to be changed.
The selection by angular phase displacement according to the cited patent, however, is not entirely devoid of shortcomings, which have limited the application of that selection device, and in particular have prevented its application to circular knitting machines operating at a high speed, as is the case with modern machines.
It should be pointed out, in fact, that whenever two or more consecutive operations of the hooked lever are required to restrain in succession two or more consecutive teeth of the toothed disk, the hook, after releasing one tooth, must be quickly inserted in the space between the released tooth and following one in order to restrain the latter, which, however, has moved in the meantime forward to the normal entrainment position consequently to the releasing of the toothed disk, thereby the insertion space for the hook with respect to the actual space between the two teeth is considerably reduced. It will be apparent, therefore, how at high speeds it becomes impossible, owing to the forces of inertia involved, to effect in a reliable manner this insertion in a space that is growing gradually smaller.
On the other hand, to increase the responsiveness of the hook for returning into the position restraining the successive or following tooth, the spring holding it in that position would have to be made stronger, which would render the releasing action of the disk yet more difficult, as this action is required to occur against the bias of this spring by means of the same toothed disk driven in the phase displaced angular position by engagement of the pin of the entrainment disk with the opening in the toothed disk. In order to facilitate this releasing, the flanks of the toothed disk teeth would have to be configurated with a greater inclination in the release direction, which would affect the restraining action reliability, this action, moreover, occurring against the bias of the spring placed between the two disks. However, since the releasing of the lever from one tooth and the re-insertion thereof to stop another tooth require accurate timing, such as to prevent for sure the premature releasing of the toothed disk, and succeed in stopping it at an equally precise time, it will be apparent how only a highly accurate dimensioning of the various components, particularly of the two springs acting in opposition to each other, can afford a consistently correct operation, and how as the operating speed is increased the problems encountered further aggravate.
Furthermore, it does not seem proper to rely on the solenoid for the task of returning the hooked lever to its inoperative position, also for those cases when the lever is required to move immediately back to its operative position in order to engage the successive tooth, since this would require an even longer time owing to the longer angular travel distance the lever would have to cover, and besides more power would be wasted in the solenoid, which in turn would require the provision of larger size solenoids, possibly too large to fit into a limited space near the selection device.
The cited Italian Patent No. 811,297 also provides for a pad or shoe type of brake rather than a hooked lever, which shoe acts on the outer periphery of the teeth, and is not required to trip each time into the space between the teeth and then move out of said space. However, it has been found that such a shoe brake device is less reliable in operation, as it does not ensure the same positive holding capacity that a hook does, and this is further enhanced by the likelihood of oil getting between the shoe friction surface and the tooth, in which event the braking action would be entirely lost, resulting in a completely erroneous selection.